Lobe switching antenna



July 1, 1947. N. E. LINDENBLAD LOBE SWITCHING ANTENNA 2 Sheets-Sheet 1Filed Dec. 10, 1943 INVENTOR 1w; E. BY

A-TIZORNEY y 1, 1947. N. E. LlNDEN-BLAD $3 LOBE SWITCHING ANTENNA FiledDec. 10,1943 2 Sheets-Sheet 2 INVENTOR IllIlLs 7. Lindenblad/ ATTORNEYF'atented July I, 1947 LOBE SWITCHING ANTENNA Nils E. Lindenblad, Rockyto Radio Corporation of of Delaware Point, N. Y., assignor America, acorporation Application December 10, 1943, Serial No. 513,691

31 Claims. 1

The present invention relates to antenna structures for radio detectingand ranging systems and, more particularly, to a lobe switching antennastructure for use at the focus of a parabolic reflector.

An object of the present invention is the provision of a focus antennafor use with a parabolic reflector.

Another object of the present invention is the provision of a directiveantenna which permits lobe switching of the beam of radiated energyWithout shifting the plane of polarization of the radiated energy.

Still another object of the present invention is the provision of a lobeswitching antenna which involves no cumbersome or delicate junctionsbetween stationary and moving portions of the associated transmissionline structure.

A further object of the present invention is the provision of a surfacecurrent antenna having no slots in the surface conductor.

Still a further object of the present invention is the provision of alobe switching antenna in which the rotating parts are mechanicallybalanced.

Still a further object of the present invention is the provision ofreactance compensation for reactance Variations with changes infrequency in the surface current antenna.

The foregoing objects, and others which may appear from the followingdetailed description, are attained in accordance with the principles ofthe present invention by utilizing an antenna structure in the form of aconductive sheet of suitable dimensions within a reactive trench. Thearea isolated from the rest of the structure by means of the reactivetrench may then be energized and serves as a radiator. This type ofantenna exhibits the very desirable characteristic of a maximumradiation in a direction normal to the plane of the sheet and ofdecreasing radiation as directions parallel to the plane of theconductive sheet are approached. The radiation falls to Zero in alldirections parallel to the plane of the sheet and there is no backradiation. The antenna may be simplified by so constructing the portionsurrounding the conductive sheet so that the radiating area issurrounded by a quarter wave wide pocket moulding of which the outeredge is attached to the sheet and the edge facing the radiating area isfree. The height of the moulding may be made a small fraction of awavelength, that is, 5 percent, or so. The height is determinedprimarily by voltage considerations. For a given amount of radiatedpower the voltage gradients developed in this type of antenna are lowerthan in heretofore known types of antennas. If desired, the radiatingarea and the surrounding mouldings may be enclosed by a window ofinsulating material extending between the facing edges of the moulding,thus protecting the structure from damage by the weather. The antenna ispreferably energized by transverse line connections inside the mouldingcavities at proper matching distance from the free edge of the moulding,

The antenna as so far described may then be located at the focus of aparabolic reflector, facing the reflector. In order to obtain a uniformprogression of the beam of radiated energy about the axis of theparabolic reflector, either one of two systems of lobe switching may beused. Thus, a displacement of the center of the total radiation for lobeswitching may be achieved by means of a pair of non-resonant shadingpatches mounted on an insulating disc rotating parallel and close to theedges of the mouldings. The shading patches may consist, for example, ofthin conductive foil cemented on an insulating disc and angularlydisplaced degrees from each other. As the disc rotates, the tWo patchessuccessively assume positions wherein they both protrude over one edgeof the same moulding and wherein one protrudes over the edge of eachmoulding. Thus four quadrant lobe switching is obtained. It will benoticed that all antenna components including the lobe switchingstructure are at substantially the same distance from the parabolicreflector with which it is contemplated the present antenna be used.Thus the characterlstic low radiation in the plane of the antennastructure itself is not aifected.

Alternatively a conductive disc of a diameter somewhat smaller thanrequired for diametric half wave tuning may be located at a distance ofthe order of a quarter wave in front of the primary radiating area. Itthus acts as a director component. Since the disc is parallel with theprimary radiating area, rotation of the disc about its center would notin any way afiect the electrical characteristics of the antenna.However, if the disc is mounted to spin eccentrically with reference tothe central axis of the primary radiating area, a progressivedisplacement of the total radiation about the axis of the antenna isobtained. The eccentrically located conductive disc should, of course,be mechanically balanced and may also be aero-dynamically balanced byenclosing it within a. circular insulating envelope rotating about itsgeometric center. 7

The present invention will be more fully understood by reference to thefollowing detailed description which is accompanied by a drawing inwhich Figure 1 illustrates in front elevational view an antennaconstructed according to the principles of the present invention, whileFigure 2 is a transverse section of Figure 1 taken along the lines 2, 2of Figure 1, and Figure 3 is another transverse section of the antennashown in Figure 1 taken along lines 3, 3, while Figure 4 is a view inperspective of a modified form of the present invention, while Figures5, 6 and '7 illustrate in perspective, and partly in section, modifiedantenna systems in which any reactance introduced into the transmissionline as the frequency applied to the antenna varies, is counterbalancedby reactance stubs connected to the transmission line at appropriatepoints, and Figure 8 is a further modification particularly adapted tobe used with wave guide energizing means.

In Figures 1 to 3, inclusive, reference numeral l indicates, generally,the radiating portion of a conductive sheet antenna. The radiatingportion is isolated from the rest of the structure of the antenna bymeans of pocket mouldings l2 and I l.

These pocket mouldings each include bottom wall portions 13 and 15attached to the sides ofradiating sheet l0 and face portions l2 and I4lying in a plane parallel to the sheet to. The ends of pocket mouldingsl2 and 14 may be closed by end plates 2, 2 and 4, 4 or they may be leftopen as desired. The width of the face portions l2 and i l of the pocketmouldings is so chosen as to be equal to one-quarter of the operatingwavelength. Since the voltage gradients developed across radiating sheetID are comparatively low even for high radiated power, the width ofmouldings i2 and I4, that is, the widths of bottom walls l3 and I needonly be a small fraction of a wavelength, that is, 5% or so. Preferably,the radiating area Ill of the antenna has an overall length of about 1wavelength and a free width between the free edges of mouldings i2 and Il of approximately one-half of the operating frequency. The antenna isenergized from a suitable source of high frequency energy (not shown) bymeans of concentric transmission line TL which .is split into twobranches, TLI and TLZ, having inner conductors l6 and If. The centerconductors I6 and I! each cross the space enclosed by one pocketmoulding and are connected to faces [2 and M, respectively. Transmissionline branch TLI has its length so chosen as to be a half wave longerthan transmission line branch TL2, the energy appearing across pocketmouldings l3 and i5 is in an opposing phase relationship. Thus, at anygiven instant the potential gradient across the half wave dimension ofradiating sheet [0 will vary from, for example, a maximum positive valueopposite the free edge of moulding l2 to a maximum negative potentialopposite the free edge of moulding i l. The potential distribution alongthe length of the radiating area I0 is substantially uniform. The pointsof connection of the inner conductors l6 and H to the faces 12 and I4 ofthe edge mouldings is so determined as to insure an impedance matchbetween the antenna and the transmission line.

The antenna as so far described has a radiation pattern characterized bya maximum radiation in a direction normal to the plane of sheet andwhich uniformly decreases in all directions as the plane of the sheet H!is approached.

The radiation is substantially zero in all directions parallel to theplane of the sheet [0 and in all directions to the rear of the sheet.Now, in order to provide a continuous progression of the beam ofradiated energy about a central axis normal to the plane of sheet iii, alobe switching structure is provided in the form of an insulating disc20 rotated by motor 22 having a shaft 23 passing through sheet H] atsubstantially its midpoint and normal to the plane of the sheet. Theinsulating disc 2i] carries on its edge at points angularly displaced bydegrees a pair of shading patches 24 and 26. The patches may be thinaluminum or other conductive foil, cemented between two thin sheetsforming disc 20. Now, as disc 29 is rotated the shading patchessuccessively assume the following effective positions: first, bothpatches 24 and 26 overlap the edge of face i2 of pocket moulding l2;then, as the rotation is continued in a clock-wise direction, shadingpatch 2 overlaps the edge of face 14' of pocket moulding M and patch 26overlaps the edge of face If; next, both patches overlap the edge offace Hi of pocket moulding M, as indicated by dotted outline 26' and 24,and patch 24. overlaps the edge of face I2, while patch 2.6 overlaps theedge of face i l. Thus, as the shading disc 20 successively assumes thefour positions outlined above, the direction of maximum response of theantenna is successively defiected into four quadrants about an axisnormal to the plane of sheet II].

In practice, the antenna may be placed at the focus of a parabolicreflector and in such position that the front surface of Sheet l0 facesthe reflector.

It will be noted that as the beam of radiant energy is caused toprogress about the axis of the parabolic reflector, all of the radiatingcomponents maintain the same distance from the parabolic antenna. Sincethere is no potential viariation along the axis of the antenna there issubstantially no radiation in directions parallel to the plane of sheetH]. In order that the displacement of the radiation center caused byshading one of each moulding by the shading patches may be of comparablemagnitude to the eiiect occurring when both patches shade one moulding,it is desirable to split each moulding at its midpoint from the freeedge to the bonded edge. These splits are shown at 28 and 30. Now, sincethe split portions are each substantially a quarter wave deep, the upperand lower halves of the pocket mouldings are substantially isolated onefrom the other. Since the inner conductors l6 and H of transmissionlines TLI and TLZ must be connected to the pocket mouldings i2 and I lat their midpoints, the inner conductors must likewise be split for adistance of a quarter Wave in order to isolate the halves of themoldings. This is indicated at 3| in the side view, Figure 3. This splitshould, likewise, be one quarter wave long.

The modification of the invention shown in Figure l utilizes the sameconstruction for the radiating sheet and pocket mouldings, a heretoforedescribed, and therefore the same reference numerals are applied as faras they are appropriate. This form of lobe switching does not requirethe division of the quarter wave pocket mouldings i2 and i l at theirmidpoints and the splits 23 and of Figure l are therefore not shownhere. The lobe switching is obtained in this modification by providing adirector component in the form of a conductive disc ii] 10- cated at adistance of a quarter wave in front of the primary radiating sheet Ill.The disc 4!) is mounted eccentrically on shaft 23 to wobble about thecentral axis of the primary radiator I 0. A continuously progressivedisplacement of the total radiation in an orbit about the central axisof sheet Ill is thus caused. The eccentrically rotating disc 40 should,of course, be mechanically balanced and it is preferable that it beaerodynamically balanced by enclosing it within a concentricallyrotating insulating envelope 42, formed, as described with reference todisc 20 of Figure 1, of a pair of thin sheets cemented together.Eccentric disc 46 may be a comparatively thin conductive foil in thepoint between the sheets forming the envelope 42.

Under some certain circumstances it may be desirable to utilize theantenna of the present invention for a wide band of frequencies. In suchcases, as the wave applied to the antenna departs from the mid frequencyof the band, it will be noted that the quarter wave mouldings on eitherside of the antenna introduce reactances into the transmission line of amagnitude and sign varying with the magnitude and sense of departure ofthe wave from the midband frequency. In order to compensate for thiswithin reasonable limits, a modified form of the invention shown inFigures 5, 6 and 7 may be used. The antenna structure in each of thesefigures is the same as has been heretofore described, and will nottherefore be described.

In the modification shown in Figure 5, resonant chambers 5i and 52 areassociated with transmission lines TLl and TL2. Chamber 5! acts as ashunt resonant circuit across transmission line TLI and resonant chamber52, across transmission line TL2. These resonant chambers are coupled tothe transmission lines each at a distance equal to one-quarter of themean operating Wavelength from the point of connection of thetransmission lines to the reactive mouldings l2 and I4, respectively.Now, if the frequency departs in one direction from that for which theantenna is designed, resonant chamber 51, for example, will introduce areactance equal in magnitude and sign to that introduced intotransmission line TLI by moulding 12. Similarly, resonant chamber 52will introduce into transmission line TLZ a reactance equal in magnitudeand sign to that introduced by moulding id. The impedance reversingcharacteristic of the quarter wave line sections between the chambersand the antenna couplings causes an exact neutralization of thereactance introduced by the departure in frequency. The resonantchambers 5i and 52 are shown in Figure 5 as having such diametraldimension as to be resonant to the mean operating frequency and they arecoupled to the transmission lines TL! and TLZ by the central conductorsl6 and I i passing through the resonant chambers and in the direction oithe electric field. It is, of course, not necessary that resonantchambers be used in these positions as any equivalent form of resonantcircuit may be used if desired, such as quarter wave line sectionsshort-circuited at one end and suitably coupled to the inner conductorof the transmission lines.

In the modification shown in Figure 6 only a single resonant chamber 53is used. Transmission lines TL! and TLZ in this modification each havean overall length equal to one quarter of the operating wavelength andtransmission line TL is coupled directly into resonant cavity 53. 'Sinceit is essential that energy applied to the mouldings l2 and M be in anoperating phase relationship, transmission lines TLI and TLZ enter theresonant chamber 53 from opposite sides, thus performing the phasereversing function. The reactance compensation occurs as described abovewith reference to Figure 5.

The modification shown in Figure '7 difiers from that shown in Figure 6only in that the resonant chamber 53 lies with its diametral dimensionsin a plane parallel to the plane of radiating sheet it instead of atright angles thereto as shown at Figure 6. The transmission lines TLIand Th2 enter the side walls of resonant chamber 53 in this modificationand are con nected to opposite phases of the resonant chamber in orderto obtain the phase reversing func tion.

Figure 8 illustrates a modification of the present inventionparticularly adapted for use with wave guide coupling means between theantenna and the desired transducer equipment.

The antenna itself is the same as described in the previous embodimentsand will, therefore, not be again described here. Obviously the lobeswitching structure of either Figure 1 or Figure 4 may be employed withthis antenna if desired,

The antenna is coupled to the transducer equipment by a wave guide WG.If the dimension of the wave guide in a direction parallel to the longdimension of the free area of sheet In is chosen to be equal to orgreater than one half of the operating Wavelength, a transverse electricwave of the lowest order may be propagated through the guide. Since thedimension of the guide perpendicular to the last mentioned dimensiondetermines the characteristic impedance of the line, it is chosen inaccordance with the operating characteristics desired.

As wave guide WG approaches the antenna, it is split into two branchesone of which terminates in the space between moulding l2 and sheet l0,and the other between moulding I l and sheet I 9. At a given instant thedirection of the electric field from l2 to ill may be in a downwarddirection while at the same instant the direction of the electric fieldwill be from Ill to Id at the other edge of the radiating sheet Iii.Thus, sheet I0 is caused to radiate in the same manner as in thepreviously described modifications.

One of the branch wave guide sections defined by the space between gh ofplate l0 and 11-1) of plate 80, it will be noticed, has a length in thedirection of wave travel of one quarter of the operating wavelength. Atone end it is coupled to the antenna, and at the other end it is coupledto a half wave compensating cavity 8| constituted by the space betweenone wall outlined by a, b, c, d and another outlined by J, e, 01. Thus,any variation in impedance introduced by the antenna into one branch bya variation in frequency is compensated for by similar variationsintroduced across the line by the compensating cavity a quarter waveaway.

Similarly, the other branch wave guide is provided with a quarter wavesection defined by plate and sheet I0 having a similar compensatingcavity 9| coupled to one end.

While I have illustrated a particular embodiment of the presentinvention, it should be clearly understood that it is not limitedthereto since many modifications may be made in the several elementsemployed and in their arrangement and it is, therefore, contemplated bythe appended claims to cover any such modifications as fall within thespirit and scope of the invention.

What I claim is:

1. A surface current antenna includin a plane conductive sheet havinghollow conductive mouldings along a pair of opposite edges and means forcoupling a transducer to said antenna including conductor means crossingthe space within said mouldings.

2. A surface current antenna including a plane conductive sheet havinghollow conductive mouldings along a pair of opposite edges, the freeedges of said mouldings extending inwardly from said opposite edges adistance equal to one-quarter of the operating wavelength and means focoupling a transducer to said antenna including conductor means crossingthe space within said mouldings.

3. A surface current antenna including a plane conductive sheet onewavelength at the operating frequency in length and width and havinghollow conductive mouldings along a pair of opposite edges, the freeedges of said mouldings extending inwardly from said opposite edges adistance such that the open area of said plane sheet has a width equalto one-half of the operating wavelength.

4. A surface current antenna including a plane conductive sheet havinghollow conductive mould-- ings along a pair of opposite edges, the freeedges of said mouldings extending inwardly from said opposite edges adistance of one quarter of the operating wavelength, the open surface ofsaid plane sheet having a width equal to one half of the operatingwavelength and an overall length of one wavelength.

5. A surface current antenna including a plane conductive sheet havinghollow conductive mouldings along a pair of opposite edges, the freeedge of said mouldings extending inwardly from said opposite edges adistance of one quarter of the operating wavelength, the open area ofsaid plane sheet having a width equal to one half of the operatingwavelength and means for coupling a transducer to said antenna includingconductor means crossing the space within said mouldings.

6. A surface current antenna including a plane conductive sheet havinghollow conductive mouldings along a pair of opposite edges, the freeedges of said mouldings extending inwardly from said opposite edges adistance of one quarter of the operating wavelength, the open area ofsaid plane sheet having a width equal to one half of the operatingwavelength and a pair of transmis sion lines each having a conductorcrossing the space within said mouldings and connected to saidmouldings.

'Z. A surface current antenna including a plane conductive sheet havinghollow conductive mouldings along a pair of opposite edges, the freeedges of said mouldings extending inwardly from said opposite edges adistance of one quarter of the operating wavelength, the open area ofsaid plane sheet having a width equal to one half of the operatingwavelength and a pair of transmission lines each having a conductorcrossing the space within said mouldings and connected to said mouldingsand a circuit resonant at the operating frequency connected across eachof said transmission lines at a distance equal to an odd multipleincluding unity of a quarter wavelength from said mouldings.

8. A surface current antenna including a plane conductive sheet havinghollow conductive mouldings along a pair of opposite edges, the freeedges of said mouldings extending inwardly from said opposite edges adistance of one quarter of the operating wavelength, the open area ofsaid plane sheet having a width equal to one half of the operatingwavelength and a pair of transmission lines each having a conductorcrossing the space within said mouldings and connected to saidmouldings, the distance from the point of each connection to the bottomwall of said mouldings being so chosen that the characteristic impedanceof said antenna matches the impedance i said transmission lines.

9. A surface current antenna including a plane conductive sheet having ahollow conductive moulding along a pair of opposite edges and a pair oftransmission lines each having an outer shell and an inner conductor,said outer shells being connected to said plane conductive sheet andsaid inner conductors each crossing the space within one of saidmouldings and connected to said mouldings substantially midway alongtheir lengths.

l0. surface current antenna including a plane conductive sheet havinghollow conductive mouldings along a pair of opposite edges, the freeedges of said mouldings extending inwardly from said opposite edges adistance equal to one quarter of the operating wavelength and a pair oftransmission lines each having an outer shell and an inner conductor,said outer shells being connected to said plane conductive sheet andsaid inner conductors each crossing the space within one of mouldingsand connected to the moulding substantially midway between its ends.

. 11. A surface current antenna including a plane conductive sheethaving hollow conductive mouldings along a pair of opposite edges, thefree edges of said mouldings extending inwardly from said opposite edgesa distance of one quarter wavelength, the open area of said plane sheethaving a width equal to one half of the operating wavelength, a pair oftransmission lines each having an outer shell and an inner conductor,said outer shells being connected to said plane conductive sheet andsaid inner conductors each crossing the space within one of saidmouldings and connected to the moulding substantially midway between itsends, and a circuit resonant at the operating frequency connected acrosseach of said transmission lines at a distance equal to an odd multiple,including unity, of a quarter wavelength from said mouldings.

12. A surface current antenna including a plane conductive sheet havinga hollow conductive moulding along a pair of opposite edges and a pairof transmission lines each having an outer shell and an inner conductor,said outer shells being connected to said plane conductive sheet andsaid inner conductors each crossing the space within one of saidmouldings and connected to said mouldings at substantially theirmidpoints, said transmission lines having a differential length equal tohalf the operating wavelength and being connected in a parallelrelationship to energy transducer means.

13. A surf ace current antenna including a plane conductive sheet havinghollow conductive mouldings along a pair of opposite edges, the freeedges of said mouldings extending inwardly from said opposite edges adistance equal to one-quarter of the operating wavelength and a pair oftransmission lines each having an outer shell and an inner conductor,said outer shells being connected to said plane conductive sheet andsaid inner conductors each crossing the space within one of saidmouldings and connected to said mouldings at substantially theirmidpoints. said transmission lines having a differential length equal tohalf the operating wavelength and being connected in a parallelrelationship to energy transducer means.

14. An antenna system including a radiating member in the form of a flatconductive sheet so energized as to provide a radiation pattern having amaximum intensity along a desired line of directivity and uniformlydecreasing intensity with increasing departure from said line, and meansfor progressively displacing said maximum intensity in an orbit aboutsaid line.

15. An antenna system including a radiating member characterized by aradiation pattern having a maximum intensity along a desired line ofdirectivity and uniformly decreasing intensity with increasing departurefrom said line, and means for progressively displacing said maximumintensity in an orbit about said line, including eccentrically rotatabledisc mounted in front of said radiating member a distance one-quarter ofthe operating wavelength, the diameter of said disc being of the orderof one-half of the operating wavelength.

16. An antenna system including a sheet radi ator and means forprogressively displacing the region of maximum radiation in an orbitabout a line normal to said sheet, including an eccentrically rotatabledisc mounted in front of said sheet radiator a distance one-quarter ofthe operating wavelength, the diameter of said disc being of the orderof one-half of the operating Wavelength.

1'7. An antenna system including a sheet radi" ator and means forprogressively displacing the region of maximum radiation in an orbitabout a line normal to said sheet, including a pair of inductive shadingpatches on an insulating disc arranged for rotation in front of andclosely adjacent said sheet radiator, said shading patches being soplaced on said disc as to successively overlap the edges of said sheetradiator.

18. A surface current antenna including a plane conductive sheet havinghollow conductive mouldings along a pair of opposite edges, the freeedges of said mouldings extending inwardly from said opposite edges adistance of one-quarter wavelength, the open area of said plane sheethaving a width equal to one-half of the operating wavelength and a pairof transmission lines each having an outer shell and an inner conductor,said outer shells being connected to said plane conductive sheet andsaid inner conductors each crossing the space within one. of saidmouldings and connected to said mouldings at substantially theirmidpoints, said transmission lines having a diiferential length equal tohalf the operating wavelength and being connected in a parallelrelationship to energy transducer means.

19. A surface current antenna including a plane conductive sheet onewavelength at the operating frequency in length and Width and havinghollow conductive mouldings along a pair of opposite edges, the freeedges of said mouldings extending inwardly from said opposite edges adistance such that the open area of said plane sheet has a width equalto one-half of the operating wavelength and means for displacing theregion of maximum effectiveness of said antenna from a line normal tosaid plane conductive sheet in an orbit about said line.

20. A surface current antenna including a plane conductive sheet havinghollow conductive mouldings along a pair of opposite edges, the freeedges of said mouldings extending inwardly from said opposite edges adistance of one-quarter of the operating wavelength, the open area ofsaid plane sheet having a width equal to one-half of the operatingwavelength and a pair of transmission lines each having a conductorcrossing the space within said mouldings and connected to said mouldingsand means for displacing the region of maximum effectiveness of saidantenna from a line normal to said plane conductive sheet in an orbitabout said line. Y

21. A surface current antenna including a plane conductive sheet havinga hollow conductive moulding along a pair of opposite edges and a pairof transmission lines each having an outer shell and an inner conductor,said outer shells being connected to said plane conductive'sheet andsaid inner conductors each crossing the space within one of saidmouldings and connected to said mouldings substantially midway alongtheir lengths and means for displacing the reion of maximumeifectiveness of said antenna from a line normal to said planeconductive sheet in an orbit about said line.

22. A surface current antenna including a plane conductive sheet havinghollow conductive mouldings along a pair of opposite edges, the freeedges of said mouldings extending inwardly from said opposite edges adistance equa] to one quarter of the operating wavelength and a pair oftransmission lines each havin an outer shell and an inner conductor,said outer shells being connected to said plane conductive sheet andsaid inner conductors each crossing the space within one of saidmouldings and connected to said mouldings at substantially theirmidpoints, said transmission lines having a difierential length equal tohalf the operating wavelength and being connected in a parallelrelationship to energy transducer means, and means for displacing theregion of maximum effectiveness of said antenna from a line normal tosaid plane conductive sheet in an orbit about said line.

23. A surface, current antenna including a plane conductive sheet havinghollow conductive mouldings along a pair of opposite edges, the freeedges of said mouldingsextending inwardly from said opposite edges adistance of one quarter of the operating wavelength, the open area ofSaid plane sheet having a width equal to one half of the operatingwavelength and a pair of transmission lines each having a conductorcrossing the space within said mouldings and connected to saidmouldings, and means for displacing the region of maximum ef fectivenessof said antenna from a line normal to said plane conductive sheet in anorbit about said line, said means including an eccentrically rotatabledisc mounted in front of said sheet a distance one-quarter of theoperating wavelength, the diameter of saiddisc being of the order ofone-half of the operating wavelength. 7

24. A surface current antenna including a plane conductive sheet havinga hollow conductive moulding along a pair of opposite edges and a pairof transmission lines each having an outer shell and an inner conductor,said outer shells being connected to said plane conductive sheet andsaid inner conductors each crossing the space within one of saidmouldings and connected to said mouldings substantially midway alongtheir lengths, and means for displacing the region of maximumeffectiveness of said antenna from a line normal to said plane conducetive sheet in an orbit about said line, said means including aneccentrically rotatable disc mounted in front of said sheet a distanceone-quarter of the operating wavelength, the diameter of said disc beingof the order of one-half of the operating wavelength.

25. A surface current antenna including a plane conductive sheet havinhollow conductive mouldings along a pair of opposite edges, the freeedges of said mouldings extending inwardly from said opposite edges adistance equal to one quarter of the operating wavelength and a pair oftransmission lines each having an outer shell and an inner conductor,said outer shells being connected to said plane conductive sheet andsaid inner conductors each crossing the space within one of saidmouldings and connect" ed to said mouldings at substantially theirmidpoints, said transmission lines having a differential length equal tohalf the operating wavelength and being connected in a parallelrelationship to energy transducer means, and means for displacing theregion of maximum effectiveness of said antenna from a line normal tosaid plane conductive sheet in an orbit about said line, said meansincluding an eccentrically rotatable disc mounted in front of said sheeta distance one-quarter of the operating wavelength, the diameter of saiddisc being of the order' of one-half of the operating wavelength.

26. A surface current antenna including a plane conductive sheet onewavelength at the operating frequency in length and width and havinghollow conductive mouldings along a pair of opposite edges, the freeedges of said mould ings extending inwardly from said opposite edges adistance such that the open area of said plane sheet has a width equalto one-half of the operating wavelength, and means for displacing theregion of maximum efiectiveness of said antenna from a line normal tosaid plane conductive sheet in an orbit about said line, said meansincludin a nonconductive rotatable disc mounted in front of said sheet,the diameter of said disc being of the order of one-half of theoperating wavelength, said disc carrying a pair of conductive shadingpatches arranged to progressively overlap a free edge of each of saidmouldings and each to overlap a free edge of one of said mouldings.

27. A surface current antenna including a plane conductive sheet havinga hollow conductive moulding along a pair of opposite edges and a pairof transmission lines each having an outer shell and an inner conductor,said outer shells being connected to said plane conductive sheet andsaid inner conductors each crossing the space within one of saidmouldings and connected to said mouldings substantially midway alongtheir lengths, and means for displacing the region of maximumeffectivness of said antenna from a line normal to said plane conductivesheet in an orbit about said line, said means including anon-concluctive rotatable disc mounted in front of said conductivesheet, the diameter of said disc being of the order of one-half of theoperating wavelength, and carrying a pair of conductive shading patchesarranged to progressively overlap a free edge" of each of said mouldingsand each to overlap a free edge of one of said mouldings.

28. A surface current antenna including a plane conductive sheet onewavelength at the operating frequency in length and width and havinghollow conductive mouldings along a pair of opposite edges, the freeedges of said mouldings extending inwardly from said opposite edges adistance such that the open area of said plane sheet has a width equalto one-half of the operating wavelength, and means for displacing theregion of maximum effectiveness of said antenna from a line normal tosaid plane conductive sheet in an orbit about said line, said meansincluding a pair of conductive shading patches arranged to progressivelyoverlap a free edge of each of said mouldings, said shading patchesbeing carried on an insulating disc mounted for rotation about thecenter of said plane conductive sheet and in a plane parallel theretoand closely adjacent said mouldings, said patches being angularly spaceddegrees on said disc.

29. A surface current antenna including a plane conductive sheet havinga hollow conductive moulding along a pair of opposite edges and a pairof transmission lines each having an outer shell and an inner conductor,said outer shells being connected to said plane conductive sheet andsaid inner conductors each crossing the space within one of saidmouldings and connected to said mouldings substantially midway alongtheir lengths, and means for displacing the region of maximumeffectiveness of said antenna from a lin normal to said plane conductivesheet about said line, said means including a pair of conductive shadingpatches arranged to progressively overlap a free edge of one of saidmouldings, said shading patches being carried on an insulating discmounted for rotation about the center of said plan conductive sheet andin a plane parallel thereto and closely adjacent said mouldings, saidpatches being angularly spaced 90 degrees on said disc.

30. A surface current antenna including a plane conductive sheet oneWavelength at the operating frequency in length and width and havinghollow conductive mouldings along a pair of opposite edges, the freeedges of said mouldings extending inwardly from said opposite edges adistance such that the open area of said plane sheet has a Width equalto one-half of the operating wavelength, and means for displacing theregion of maximum effectiveness of said antenna from a line normal tosaid plane conductive sheet about said line, said means including a pairof conductive shading patches arranged to progressively overlap a freeedge of each of said mouldlugs and each to overlap a free edge of one ofsaid mouldings, said shading patches being carried on an insulating discmounted for rotation about the center of said plane conductive sheet andin a plane parallel thereto and closely adjacent said mouldings, saidpatches being angularly spaced 90 degrees on said disc, each of saidmouldings having a quarter Wave split at substantially its midpoint.

31. A surface current antenna including a plane conductive sheet havinga hollow conductive moulding along a pair of opposite edges and a pairof transmission lines each having an outer shell and an inner conductor,said outer shells being connected to said plane conductive sheet andsaid inner conductors each crossing the space within one of saidmouldings and connected to said mouldings substantially midway alongtheir lengths, and means for displacing the region of maximumefiectiveness of said antenna from a line normal to said planeconductive sheet in an orbit about said line, said means including apair of conductive shading patches arranged to progressively overlap afree edge of each of said mouldlugs and each to overlap a free edge ofone of said mouldings, said shading patches being carried 13 14 01']. aninsulating diSC mounted for rotation about REFERENCES CITED the centerof said plane conductive sheet; and in a-plane parallel thereto andclosely adjacent said The li win references are of record in themouldings, said patches being angularly spaced file Of'thIS Dat ti g0degrees on tsaid disc, ezlz ih gt szicil; mtgufiiinis 5 FOREIGN PATENTSaving a quar er wave sp1 a su s an 1a y 1 s midpoint, Number CountryDate NILS LINDENBLAD 450,484 Great Britain July 20, 1936

